The project goal is to understand the regulatory mechanisms which drive a complex developmental process: deposition of yolk into eggs of the fruit fly, Drosophila melanogaster. This involves hormonal stimulation of the three yolk polypeptide (YP) genes, YP secretion, Yp sequestration into the developing oocyte, followed by localization of the YPs into yolk granules and their utilization to nourish the embryo. The Yp genes are expressed in female, but not male fat body, and in the ovarian follicle cells, and they are regulated by both juvenile hormone and 20-hydroxyecdysone. Two questions are attacked in this proposal: (1) What are the cisacting informational signals in the DNA within or surrounding a set of genes which result in their expression at the correct developmental stage, in the proper cells, and in the appropriate sex? And 2) how do informational signals in the yolk polypeptides themselves direct their complicated history, including post-translational processing, secretion, sequestration, localization and utilization? Both questions will be addressed using in vitro mutagenesis of cloned copies of the Yp genes, followed by their introduction into fly chromosomes by P-element mediated transformation. The studies are important to health since an appreciation of gene regulation during normal development of higher organisms will better enable us to understand how gene expression is altered in the development of birth defects or in the formation of malignant tumors. Furthermore, the mechanism of secretion is important in human diseases, such as I-cell disease; and the mechanisms of protein sequestration are crucial for an understanding of the role of lipoproteins in cardiovascular disease. Finally, an understanding of fly reproductive physiology can help in the design of safer, more highly targeted, and more effective insecticides.